This invention relates to sound reproduction and more particularly to sound reflective and sound reproduction systems employing reflective surfaces.
Sound reproduction systems using passive, reflective surfaces in addition to active sound sources such as speakers are not unknown. By "speaker" or "loudspeaker" is meant one sound source or a system of several, each contributing a part of the audible frequency range. In the past, individual speaker enclosures have employed reflective elements internally to direct sound in one direction or another. Speakers have been suggested to direct sound against nearby walls for reflection back to a listening area. Sounding boards are known for use by instrumentalists to project sound either to an audience's listening area or to studio microphones. Various architectural acoustic elements have been employed or suggested to enhance the acoustical characteristics of auditoriums. Also, in connection with projection screens for motion pictures or television, sound reflecting surfaces have been suggested to associate more closely the sound track or audio portion of the program with the visual presentation. In high-fidelity sound reproduction systems, the use of nonarchitectural sound reflectors spaced from a speaker to redirect sound back towards the listener has been virtually unexplored.
The loudspeaker industry has for a long time made attempts to provide the listener with the kind of sound experienced under real-life conditions. The familiar stereo loudspeaker systems have been commercially successful because they went a long way towards realistic sound when compared with the original monaural loudspeakers. However, insofar as is known, the prior art has not provided a system of any kind which gives the listener the feeling of acoustical space and depth and scale which in an almost unexplainable way characterizes live sound.
Such attempts have included stereo loudspeaker systems wherein two speakers were pointed towards convexly curved surfaces for the purpose of distributing the sound and eliminating the well-known effect of the sound coming from more or less point sources. An example is the Ranger U.S. Pat. No. 3,065,816. Particularly for the reproduction of low-frequency sound components, reflective arrangements have been proposed, but it is generally conceded that the result has been an undesirably blurred sound reproduction.
One interesting example of the use of reflection for the purpose of achieving more realistic sound, is provided by the Karlson U.S. Pat. No. 2,896,736, July 28, 1959, proposing the use of a loudspeaker in an especially designed enclosure and pointed towards a wall for the purpose of obtaining considerably greater angular dispersions of sound than the typical 90.degree. to 120.degree. sound dispersion which the patent states is characteristic of conventional conical loudspeakers radiating directly into an air space. This patent makes various proposals one of which is to reflect the sound from the specially enclosed loudspeaker via differently curved surfaces, such as elliptical, hyperbolic, etc. This patent states that such curved surfaces permit projection of sound over considerable distances with minimal losses.
Little attention has been given to the effects of the surface of a reflector. In acoustics, whereven roughness or surface irregularities have been provided, they have been associated with sound absorption, not with sound reflection. The dispersive effect of surface roughness or irregularity has been largely or wholly ignored relative to sound reproduction systems.
In the reproduction of sound a recurrent phenomenon has been differences in the angle of dispersion of the sound for various frequencies in the audible range. Ordinarily the base frequencies are more widely dispersed and the higher audible frequencies are more narrowly dispersed. This characteristic is called herein "beaming" by virtue of the narrower or beam-like projection or cone of the higher frequencies. Again, as far as is known, there has been no attempt to resolve this recurrent difficulty by attention to the surface characteristics of a reflector.